This invention relates to a load monitor.
In particular, the invention concerns a tension monitor and it will be in relation to the monitoring of tension during the installation of electrical power cables that this invention will be described. It should be appreciated that this is by way of example only and that the monitor of the invention may be used for other purposes. For example, the monitor of the invention may be used for remote crane load indication and to monitor the compressive force applied to an article.
Load monitors are known and have variously been called force gauges or dynamometers. Such monitors are manufactured by M & W Engineering (Denmark), PIAB (Sweden) and ARNCO CORP (U.S.A.).
The M & W monitor had oppositely directed attachment portions and incorporated a load cell. An output display was visible on the housing of the monitor and remote reading was possible by securing a cable between the monitor and an optional remotely located control box. The cable disclosed was 10 meters in length.
The PIAB monitor also had a display for in situ reading. For remote reading the monitor was provided with a built-in potentiometer for transmitting a signal via a cable to a receiving instrument.
Such load monitors have a wide variety of uses in lifting, pushing and hauling applications. It has been found that in the laying of electrical cables in conduits are has to be taken to ensure that the cable is not subjected to undue tension as this can lead to damage to the cable. To lay electrical cables a capstan drive or winch was employed to wind in a winch cable to draw the electrical cable through the conduit. In the past attempts were made to monitor the tension applied to the winch cable. However, the tension to which the winch cable may be subjected need not necessarily correspond to the tension to which the electrical cable is subjected. U.S. Pat. No. 4,692,063 discloses a system for monitoring cable tension.
U.S. Pat. No. 4,461,459 discloses an apparatus for and a method of measuring tension in a pull line for an electrical cable. Clearly, where the electrical cable is underground or within a duct, remote readings of the tension are required. U.S. Pat. No. 4,461,459 discloses three ways in which the tension signal from the apparatus may be made available remotely of the apparatus. One way involved the use of a long pull tape between the apparatus and a remote receiver. The pull tape included conductors along which a tension indicative signal was conducted. The specification also proposed the use of an audio transducer and a microphone. This was not always practical because of the environment through which the electrical cable was drawn or the distances involved.
The final proposal required the presence of a separate conductor adjacent the duct or conduit through which the electrical cable was to be drawn. The apparatus included a transmitter for inducing tension indicative signals into the separate conductor. The separate conductor had a receiver associated with it. This proposal required the presence of a separate conductor and this was not always the case or possible to achieve.